Morphological and behavioral antipredatory adaptations of decapod zoeae

Summary Zoeae of some species of estuarine decapods are retained in the estuary throughout development while others are exported into nearshore coastal waters. The horizontal migrations of decapod zoeae to coastal waters may have evolved to reduce the probability of encountering planktivorous fishes which are most abundant in the estuary. If so, then the morphological vulnerability of zoeae to fish predation should be inversely related to the number of predators occurring where they develop. Six species of estuarine decapod zoeae were offered to Menidia menidia and Fundulus heteroclitus. The behavioral interactions were observed to determine the prey's vulnerability to predation, and the mode of operation and relative effectiveness of their defenses. Feeding trials and behavioral observations both demonstrated that M. menidia 6–16 mm long preferred Uca minax and Callinectes sapidus zoeae, which are exported from the estuary, to Rhithropanopeus harrisii, Sesarma reticulatum and Palaemonetes pugio, which are retained within estuaries. Pinnotheres ostreum zoeae develop in the lower estuary and fish demonstrated an intermediate preference for the zoeae. Menidia menidia 20–40 mm long showed similar preferences for R. harrisii S. reticulatum, P. ostreum and U. minax as did small silversides. Large-mouthed demersal fish, Fundulus heteroclitus 6–10 mm long, also preferred U. minax to R. harrisii, but more readily preyed on zoeae than did M. menidia. The exported species of zoeae have shorter spines and smaller bodies than do retained zoeae, except P. ostreum which is small, spineless and passively sinks when attacked by fish. Other retained species of zoeae also have postcontact behavioral defenses which enhance the effectiveness of their morphological defenses. Zoeae do not evade attacks by fishes, but fishes quickly learned to avoid zoeae, which increases the effectiveness of the zoeae's antipredatory adaptations.     

Interaction of hemopexin with Sn-protoporphyrin IX, an inhibitor of heme oxygenase. Role for hemopexin in hepatic uptake of Sn-protoporphyrin IX and induction of mRNA for heme oxygenase

Sn-protoporphyrin IX (SnPP), an inhibitor of heme oxygenase and a potential therapeutic agent for neonatal hyperbilirubinemia, is bound tightly by hemopexin. The apparent dissociation constant (Kd) at pH 7.4 is 0.25 +/- 0.15 microM, but estimation of the Kd for the SnPP-hemopexin complex is hampered by the fact that at physiological pH SnPP exists as monomers and dimers, both of which are bound by hemopexin. SnPP is readily displaced from hemopexin by heme (Kd less than 1 pM). The hemopexin-SnPP interaction, like that of heme-hemopexin, is dependent on the histidine residues of hemopexin. However, as expected from the differences in the coordination chemistries of tin and iron, the stability of the histidyl-metalloporphyrin complex is lower for SnPP-hemopexin than for mesoheme-hemopexin. Nevertheless, when SnPP binds to hemopexin, certain of the ligand-induced changes in the conformation of hemopexin which increase the affinity of the protein for its receptor are produced. Binding of SnPP produces the conformational change in hemopexin which protects the hinge region of hemopexin from proteolysis, but SnPP does not produce the characteristic increase in the ellipticity of hemopexin at 231 nm that heme does. Competition experiments confirmed that human serum albumin (apparent Kd = 4 +/- 2 microM) has a significantly lower affinity for SnPP than does hemopexin. Appreciable amounts of SnPP (up to 35% in adults and 20% in neonates) would be bound by hemopexin in the circulation, and the remainder of SnPP would be associated with albumin due to the latter's high concentration in serum. Essentially no non-protein-bound SnPP is present. Importantly, SnPP-hemopexin binds to the hemopexin receptor on mouse hepatoma cells with an affinity comparable to that of heme-hemopexin and treatment of the hepatoma cells with SnPP-hemopexin causes a rapid increase in the steady state level of heme oxygenase messenger RNA. These results show that hemopexin participates in the transport of SnPP to heme oxygenase and in its regulation by SnPP.     

Dr. Lucid's word rounds: IMRAD on the wards.

The classic site for paracentesis in generalized ascites is in the left lower quadrant of the abdomen at a position equivalent to McBurney''s point. Its use has an average success rate of 58%, depending on the amount of liquid. To assess the efficacy of paracentesis at this site and to establish the ideal site for blind puncture, we studied 27 consecutive patients with ascites detected by abdominal ultrasonography. The amount of ascites was graded from 1 to 4. Free fluid had accumulated mostly in the perihepatic region, then around the bladder and in the right paracolic gutter, and finally in the left flank. In six of the eight patients in whom fluid was found in the left or right flank, air-filled bowel loops were observed between the abdominal wall and the fluid, in the expected path of a blind puncture. These findings suggest that the safety and efficacy of paracentesis would be greatly improved by ultrasonographic guidance.     

Active site alanine mutations convert deubiquitinases into high‐affinity ubiquitin‐binding proteins

A common strategy for exploring the biological roles of deubiquitinating enzymes (DUBs) in different pathways is to study the effects of replacing the wild‐type DUB with a catalytically inactive mutant in cells. We report here that a commonly studied DUB mutation, in which the catalytic cysteine is replaced with alanine, can dramatically increase the affinity of some DUBs for ubiquitin. Overexpression of these tight‐binding mutants thus has the potential to sequester cellular pools of monoubiquitin and ubiquitin chains. As a result, cells expressing these mutants may display unpredictable dominant negative physiological effects that are not related to loss of DUB activity. The structure of the SAGA DUB module bound to free ubiquitin reveals the structural basis for the 30‐fold higher affinity of Ubp8^C146A for ubiquitin. We show that an alternative option, substituting the active site cysteine with arginine, can inactivate DUBs while also decreasing the affinity for ubiquitin.